Process of manufacturing iron tetracarbonyl



Patented Aug 29, 1933 I t N T .STATE Calii'., a corporation of Delaware Application January ,12, 1931 Serial No. 508,386 I e'ciaims. c1! 23-203) Thislin vention relates to a process of manu More facturing iron tetraca'rbonyl, Fe(CO)4.

particularly this inventionirelates to,a simple and .efiicient process of producing irontetra- 5- carbonyl directly from iron pentacarbonyl.

Heretofore in the manufacture. of irontetra carbonyl it has been necessary first to prepare iron pentacarbonyl and'then prepare the iron tetracarbonyl from Ithefenneacarbonyl. Inacfrom the reaction vessel as a gas or vapor and then may besubsequtntlycdndnsed to' afliquid at atmospheric temperwhich'iorm it exists at'ures and pressures;

Durin'gjthe preparation of iron pentacarbonyl, temperatures of from about350 F. to"400 F; may be employed. The iron pentacarb'onyl thus produced is unstable in the presence, of light, decomposing to yield a compound known as iron .enneacarbo'nyl, Fez (CO) 9, which is precip I 'itated as an orange-red insoluble solid. Carbon monoxide is evolved' in the decomposition and such decomposition is rapidin'bright light but slowly reversible in the dark, with the reformation of .the pentacarbonyl.

Iron tetracarbonyl,'Fe(CO)4', may be formed from the enneacarbonyl by heating the enneacarbonyl in the presence. of ether,toluene, trig ethylamine or light petroleum oils to temperatures not exceeding about 212 F. A bright green solution is, formed when'toluene is employed for example, and upon cooling the mix- 40 ture under'proper conditions, green" crystals of the tetracarbonyl may be obtained. These iron carbonyls,.and particularly iron tetracarbonyl, can be advantageously employed in motor fuels for permitting said fuels to operate at increased .45 compression ratios in internal combustion engines. V

An object of this invention is to disclose and provide a process of manufacturing iron tetra- 1 V u may be used for the extraction, the rated solu-v carbonyl directly from the pentacarbonyl without then'ecessity of for ming the enneacarbonyl as an intermediate. 1 V Another object is to disclose and provide a simple and rapid method of manufacturing iron tetracarbonyl. H k

A still further object is to lose and provide iron pentacarbonyl.

manufacturing conditions under which 7 iron tetracarbonylmmay. be produced directly irom These and other. objects and advantagesg of this invention will become apparent to those 50 skilled in the arti from'the;following detailed Y h i description of the preferred mode of operationf iron nonacarbonyl or iron enneacarbonyl from and all modifications' thereon It is to be'understood that the invention is;

not limited to theprecise steps employed nor to the use of the, specific materials particularly stated herein, as those skilled in the' art will readily understand the various modifications and substitutions of materialwhich can be employed in adapting this invention to the manufacture of other metallic carbonylsi under various oper-. atingconditions.

In carrying out theinvention, iron penta-' carbonyl in liquid form or in gaseous term, or a solution of iron] pentacarbonyl' in a suitable organic solvent such as benzene, ether or gasoline,

is mixedwith an alkaline solution and the agitationlis continuedluntil :the pentacarbonyl is completely or substantially completely dissolved in the alkaline solution. r

When pentacarbonyl in gaseous form is employed, it may be repeatedly passed through an alkaline solution until the desired quantity of v the pentacarbonyl is dissolved in such alkaline solution. u

A solution'of pentacarbonyl in an aqueous liquid is eviden'cedby the deepening in color of the alkaline solution to anamber shade and by the lightening in color of the organic solvent if a solution of the pentacarbonyl was originally used. :A solution of the pentacarbonyl may also be evidenced by thedisappearance of the immiscible layer of pentacarbonyl when no organic solvent w as originally employed. 1

The .alkalinefsolution in which the pentacarbonyl is dissolved may be aqueous or alcoholic. The alkaline solutions used sh ould pref: erably be five {per cent or more. in strength as the extraction of the pentacarbonylj is slower. in more dilute solutions and larger amounts of liquid must therefore be. handled to no advantage in the process. Instead of aqueous alkaline. solutions, however, alcoholic alkalinef solutions in alcohol. v The alkali used in the alkaline solution is preferably strong alkali, such. as fsoclium or po- 110 tassium. Weaker basesQsuch as ammonium hydroxide, may also be employed but the rate at" which the pentacarbonyl is dissolved in such weaker bases is much lower than alkalis are used.

The mixture-of iron pentacarbonyl and or alkaline solution may have to be agitated for an appreciable period of time. Agitation for an hour or more may be required, depending upon when strong the type-of rapidity or agitationpused as well as the character of the "alkaline solution em-- ployed. The extraction may be carried out at" atmospheric temperature and pressure, although the use of higher temperatures increasesthe rate of solution of the pentacarbonyl in the alkali. When higher temperatures are employed, however, pressures above atmospheric are desirable so as to prevent loss of thepentacarbonyl (and of the organic solvent, if pres--. ent) by evaporation and to prevent decomposition of 'therpentacarbonyl; When a large amount of iron pentacarbonyl is dissolved in an aqueous caustic solution and'the solution is allowed to stand for several hours,

-" orange colored crystals willseparate out. W hen dry,'the'se crystals take fire spontaneously on exposure to the air,v leaving ferric oxide. High concentrations of iron pentacarbonyl in the caustic solutions should therefore be avoided, or if high concentrations are produced, precaution should be taken against the accidental separation and drying of these crystals. The alkaline-solutionof the pentacarbonyl made as described hereinabove, is now acidified by the addition of an acid .and preferably a-strong acid, such as hydrochloric or sulfuric acid. A gas, probably carbon monoxide, is. evolved upon the acidification of the alkaline solution of iron carbonyl, and iron tetracarbonyl is precipitated as an amorphous 'green solid.

*The'reaction is completed when the amber color of the pentacarbonyl 7 solution disappears entirely. When strong acids, such as hydrochloric or sulfuric,'are used for the precipitation of'iron tetracarbonyl, it may be desirable to cool the solution during acidification so asto prevent an appreciable rise in temperature The iron tetracarbonyl'so produced may then.

be separatedirom the liquid by any convenient means, such as filtration, centrifugal separation or settling. Instead-of employing these modes of separating the tetracarbonyl from the solution, the tetracarbonyl may be extracted by.

f means of an organic solvent, such as benzene,

' toluene or light petroleum oils such as gasoline.

If it is intended that the tetracarbonyl be employed subsequently in solution, then the ex traction of the tetracarbonyl by means of a solvent is an obviously convenient procedure.

The tetracarbonyl. produced. in accordance with the method described hereinabove, is practically chemically pure, and it is not necessary to purify it further for all ordinary purposes.

Weak acids, I such as acetic or butyric, are preferably not'employed in acidifying the alkaline pentacarbonyl solution as upon the addi tion of weak acids, the iron tetracarbonyl will not be formed as an insoluble precipitate which can 'bereadily removed from the solution by chemical means. The gas above referred to, probably carbon monoxide, isevolved, however.

When weak acids are used, instead of the formation of tetracarbonyl as an insoluble precipitate, a deep red solution results and: iron tetracarbonyl may be extracted from this deep red solution with gasoline, benzene or other suitable solvent. It is preferred to carry out the acidification with a strongeraoid, however, and to precipitate the tetracarbonyl as a 'solid. In actual practice, the process has been conveniently carried out-as follows: Nine parts of a iron pentacarbonyl, eitheras the compound itself orin solution in, an organic solvent, are dissolved in ten percent sodium hydroxide solution ;.cont aining four parts NaOI-I. This solution is. acidifiedwith twenty-five per cent sulfuric or hydrochloric acid which is added slow- 1y, to the solution with accompanying cooling. The precipitated iron tetracarbonyl is then removed from the solution in any desired manner.

It will thus [be seen that the entire process is a simple one and easily carried out, without T the necessityof highly skilled chemical control.

Alkalis of a great range of concentration may be used in dissolving the pentacarbonyl; acids of a great range of concentration may be used in the aci dification"and precipitation of the tetracarbonyl. The process" is characterized by the fact that the enneacarbonyl need-not be formed at all. Moreover, a product; of greater purity is produced, as, by theexisting processes .some pentacarbonyl contaminates the carbonyl in an alkaline liquid, acidifying the solution thus formed by the addition of a strong foo . bonyl, comprising forminga s0lution of' penta acid, and separating irontetracarbonylffrom the acidified solution.

3. A process of manufacturing iron 'tetracar-L bonyl, comprisingrformin'g asolution of 'penta carbonyl in an alkaline liquid, agitating the mix-.

ture, acidifying the alkaline solution by "the ad "dition of a mineral acid, and then separating iron tetracarbonyl from the acidifiedsolution.

4. A process of manufacturingiron'tetracarbonyl, comprising dissolving iron'pentacarbonyl in an alkaline solution with agitation, acidifying theresulting'solution with 'a mineral acid, and

extractingiron tetracarbonyl from the acidified solution with an' organic solvent.

('5. A processlof manufacturing iron tetracarbonyl, comprising dissolving iron pentacarbonyl inan alkaline solutionwith agitation at a pressuresufiicient to prevent-decomposition of'iron pentacarbonyl, acidifying thealkaline solution with a mineral acid, and th'ense'parating iron tetracarbonyl from the acidified solution. 1

" 6. Aprocess of manufacturing iron tetracarbonyl,. comprising dissolving iron pentacarbonyl in an alkaline solution,"acidifying themixture with mineral acid to precipitate iron tetracarbonyl, and then separating iron tetracarbonyl from the acidified solution.

7. A process of manufacturing iron tetracarbonyl, comprising agitating a solution of iron pentacarbonyl in an organic solvent withja solution of a strong "base, acidifying the resulting alkaline solutionwith strong acid, and extracting the acidified solution with an cream vent for iron tetracarbonyl.-

1,924,453 v o 8. A process of manufacturing iron tetracan bonyl, comprising dissolving iron pentaoarbonyl bonyl, comprising forming a solution of iron pen! tacarbonyl in an alcoholic alkaline liquid, acidifying the mixture thus formed with strong acid,

and then separating iron tetracarbonyl from such acidified solution.

in an alkaline's'olution, acidifying the alkaline solution thus formed with a. mineral acid, coolingthe acidified fmixture, and separatingiron tetracarbonyl from theacidified solution. 

